@siguza @jerry

Via Mastodon, @jerry asked, "Does anyone know of a good how to guide for non-technical people that explains how to clean up and secure their iPhones and iCloud accounts if they are suspected of being compromised?"

Not having found such a guide, here is a summary of the of the substantive responses to @jerry's question; from contributors @siguza, @suzannealdrich, @unknown8bit, @cshishido & @rmd1023

How to clean up and secure iPhones and iCloud accounts

There are many ways an iPhone or its iCloud account can be compromised. If the risk is primarily a compromise of information, rather than an infection of malware, the following are the primary steps to re-secure things and deal with potential data leaks/oversharing.

Securing the information on an iPhone also means securing iCloud ... and all the *other* devices using that iCloud account as well.

Do not use these steps if your iPhone is under enterprise mobile device management (MDM). Have your organization's IT security specialists handle this (at least some of which they will want to do remotely, through MDM).

Also, if you think your iPhone and/or iCloud account could be compromised via an APC, these steps will only be a beginning of what you'll need to do. Seek expert help for what else may be necessary.

1. If your iOS is out of date, update to the latest version and restart ASAP. [This step alone can often clear malware embedded in the iOS file system.] If iOS up-to-date, just restart to (at least temporarily) clear any in-memory malware. If your iPhone is so old that it cannot be updated to the current version of iOS, replace it with a new iPhone which can.
2. Change your iPhone's passcode at Settings > Face (or Touch) ID & Passcode. Do not use a simple 4-number PIN, use an 8 (or more) character passcode instead. Write it down, on paper, so you won't forget it -- do not store it electronically.
3. While on that Settings page, turn on your Face (or Touch) for everything you can, to reduce your need to use that passcode to a minimum.
4. Using Safari, log into "appleid.apple.com" with the Apple ID you use with iCloud, and change its password. Write that down on paper.
5. While logged here, check which Devices use that iCloud. Remove any that you don't recognize, no longer have, or otherwise would not want using it. Write down -- on paper -- the list of names of the Devices you *do* want using iCloud (you'll be changing all their passcodes, and will want to write those down next to each name).
6. Update your iPhoneto use the new Apple ID it uses in Settings > your name > Sign-In & Security > Change Password.
7. On each of the other device on the list, change its passcode to something different, using better than 4-digit PINS wherever possible), using a different passcode for each device. Write all of those new passcodes down.
8. Then update the Apple ID password the device. It could ask for either the iCloud password or Apple ID password. It's the same thing. [If your Apple ID's name is an email address you something like user@mac.com, user@me.com or user@icloud.com then that new iCloud password is *also* the new password for that email account, which Apple devices should pick up automagically. If the name of your Apple ID/iCloud account is that of some some 3rd-party email account, that email password will remains whatever it was. Optionally, change that password separately.]
9. Pm your iPhone, go to Settings . Privacy & Security > Safety Check > Manage Sharing & Access to see and set which people and apps can access your information and review your account security. Briefly: sharing information between your iPhone and other devices using the same iCloud is OK, but be skeptical of any other sharing. [The easiest way to compromise your iPhone is to over-share.]

[Optionally, also see:
support.apple.com/g...
(where Safety Check is the first thing to do), and complete these three additional checklists as well: Limit access, Manage location, and Stop Sharing. Also optional, but desirable: change the passwords you use with every 3rd-party app and for every web site you use a password for. Do save all of these username/password pairs electronically in a password manager [Apple's new Passwords app can be used for this -- and its database can safely be shared among your Apple devices using iCloud. 1Password can be used the same way -- it can be shared via its own server. Whatever password manager you use, make sure it supports passkeys as well -- because sooner or later you will be wanting to upgrade your username/password pairs to passkeys ...]

10. The next and last step we recommend in this guide is to protect iCloud itself: turn on Advanced Data Protection for your iCloud data. Read up on it first, at:
support.apple.com/g...
... and also know that Advanced Data Protection will severely limit what can be done when you log in to iCloud.com. [If you feel uncomfortable doing this step, seek expert help [e.g., with an Apple Genius Bar appointment.]

Now you just need to always & consistently use your iPhone and other devices securely! There's lots and lots of advice on the Internet about how to do that ...

[If you could be targeted by an APT or have especially critical data on your iPhone and/or iCloud, all the above is only the beginning of what to do. Seek professional help! At your company, or at least at an Apple Genius Bar. As a preview, you will probably need to secure your Wifi network(s): rename, set a new password, and check the security settings of each WiFi network you use, as well as checking the security settings for any and ALL other devices using those networks (and make sure your iPhone only uses those networks); opt out of your cell carrier's email-to-text gateway; turn off "previews" of email, messages, and web page contents; pay for iCloud+ for extra storage and its extra security features: Private Relay and Hide My Email; start using a new, more secure email provider if necessary; and activate Lockdown Mode on your devices.]